Effects of SnO2 Passive Film and Surface Micro-Galvanic Corrosion on the Corrosion Behavior of as-Extruded Mg-9Li-5Al-xSn Alloys

The effects of the SnO2 passive film and micro-galvanic corrosion on the corrosion behavior of as-extruded Mg-9Li-5Al-xSn (x = 0, 0.5 and 1.0 wt.%, LA95) alloys were investigated. As the Sn content increased from 0.5 to 1.0 wt.%, Sn was first dissolved and then precipitated Mg2Sn. The SKPFM results indicated that the Volta potential difference of AlLi/α-Mg, Mg2Sn/α-Mg and β-Li/α-Mg was 370, 200 and 120 mV, respectively. The electrochemical experiment results indicated that the corrosion resistance of LA95–0.5 wt.% Sn alloy was significantly improved (98.7%), which can be attributed to the local protective film containing SnO2 that prevented the contact of the electrolyte solution and the cathode. In the LA95–1.0 wt.% Sn alloy, excessive Sn precipitated Mg2Sn weakening the protective effect of SnO2 film. The corrosion mechanism after Sn addition in as-extruded LA95-xSn alloy was discussed.